After their launch in 1999, Chandra and XMM-Newton provided the required sensitivity to detect the X-ray emission from large samples of high-redshift QSOs, and, in turn, investigate their accretion properties. Starting from 2002, tens of \(z>6\)  QSOs have been either targeted by or serendipitously covered with X-ray observations, and their number is expected to increase in the next years.
Fig. REF  presents the distribution of the exposure times of X-ray observations covering the 39 \(z>6\)  QSOs for which such data has been published (before February 2022, see Tab. REF ), including two QSOs pointed with Swift/XRT. Most of the available datasets consist of tens of ks observations, and a few QSOs have been covered with \(>100\)  ks, up to the \(\approx 500\)  ks coverage of J1030+0524 ([1]}). In addition, the on-going extended Roentgen Survey with an Imaging Telescope Array (eROSITAhttps://erosita.mpe.mpg.de/edr/, [2]}, [3]}) all-sky survey has already started contributing to increase the number of X-ray detected \(z>6\)  QSOs ([4]}).
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